system.java

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/*
 * @(#)System.java	1.124 06/10/10
 *
 * Copyright  1990-2008 Sun Microsystems, Inc. All Rights Reserved.  
 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER  
 *   
 * This program is free software; you can redistribute it and/or  
 * modify it under the terms of the GNU General Public License version  
 * 2 only, as published by the Free Software Foundation.   
 *   
 * This program is distributed in the hope that it will be useful, but  
 * WITHOUT ANY WARRANTY; without even the implied warranty of  
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU  
 * General Public License version 2 for more details (a copy is  
 * included at /legal/license.txt).   
 *   
 * You should have received a copy of the GNU General Public License  
 * version 2 along with this work; if not, write to the Free Software  
 * Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  
 * 02110-1301 USA   
 *   
 * Please contact Sun Microsystems, Inc., 4150 Network Circle, Santa  
 * Clara, CA 95054 or visit www.sun.com if you need additional  
 * information or have any questions. 
 *
 */

package java.lang;

import java.io.*;
import java.util.Properties;
import java.util.PropertyPermission;
import java.util.StringTokenizer;
import java.security.AccessController;
import java.security.PrivilegedAction;
import java.security.AllPermission;
import sun.net.InetAddressCachePolicy;
//import sun.reflect.Reflection;
import sun.security.util.SecurityConstants;
import com.sun.cdc.config.PackageManager;
import com.sun.cdc.config.DynamicProperties;
import com.sun.cdc.config.PropertyProvider;

/**
 * The <code>System</code> class contains several useful class fields
 * and methods. It cannot be instantiated.
 * <p>
 * Among the facilities provided by the <code>System</code> class
 * are standard input, standard output, and error output streams;
 * access to externally defined "properties"; a means of
 * loading files and libraries; and a utility method for quickly
 * copying a portion of an array.
 *
 * @author  Arthur van Hoff
 * @version 1.114 05/18/01
 * @since   JDK1.0
 */
public final class System {

    /* First thing---register the natives */
    /* No need to do this if ROMized
    private static native void registerNatives();
    static {
        registerNatives();
    }
    */

    /** Don't let anyone instantiate this class */
    private System() {
    }

    /**
     * The "standard" input stream. This stream is already
     * open and ready to supply input data. Typically this stream
     * corresponds to keyboard input or another input source specified by
     * the host environment or user.
     */
    public final static InputStream in = nullInputStream();

    /**
     * The "standard" output stream. This stream is already
     * open and ready to accept output data. Typically this stream
     * corresponds to display output or another output destination
     * specified by the host environment or user.
     * <p>
     * For simple stand-alone Java applications, a typical way to write
     * a line of output data is:
     * <blockquote><pre>
     *     System.out.println(data)
     * </pre></blockquote>
     * <p>
     * See the <code>println</code> methods in class <code>PrintStream</code>.
     *
     * @see     java.io.PrintStream#println()
     * @see     java.io.PrintStream#println(boolean)
     * @see     java.io.PrintStream#println(char)
     * @see     java.io.PrintStream#println(char[])
     * @see     java.io.PrintStream#println(double)
     * @see     java.io.PrintStream#println(float)
     * @see     java.io.PrintStream#println(int)
     * @see     java.io.PrintStream#println(long)
     * @see     java.io.PrintStream#println(java.lang.Object)
     * @see     java.io.PrintStream#println(java.lang.String)
     */
    public final static PrintStream out = nullPrintStream();

    /**
     * The "standard" error output stream. This stream is already
     * open and ready to accept output data.
     * <p>
     * Typically this stream corresponds to display output or another
     * output destination specified by the host environment or user. By
     * convention, this output stream is used to display error messages
     * or other information that should come to the immediate attention
     * of a user even if the principal output stream, the value of the
     * variable <code>out</code>, has been redirected to a file or other
     * destination that is typically not continuously monitored.
     */
    public final static PrintStream err = nullPrintStream();

    /* The security manager for the system.
     */
    private static SecurityManager security = null;

    /**
     * Reassigns the "standard" input stream.
     *
     * <p>First, if there is a security manager, its <code>checkPermission</code>
     * method is called with a <code>RuntimePermission("setIO")</code> permission
     *  to see if it's ok to reassign the "standard" input stream.
     * <p>
     *
     * @param in the new standard input stream.
     *
     * @throws SecurityException
     *        if a security manager exists and its
     *        <code>checkPermission</code> method doesn't allow
     *        reassigning of the standard input stream.
     *
     * @see SecurityManager#checkPermission
     * @see java.lang.RuntimePermission
     *
     * @since   JDK1.1
     */
    public static void setIn(InputStream in) {
	checkIO();
	setIn0(in);
    }

    /**
     * Reassigns the "standard" output stream.
     *
     * <p>First, if there is a security manager, its <code>checkPermission</code>
     * method is called with a <code>RuntimePermission("setIO")</code> permission
     *  to see if it's ok to reassign the "standard" output stream.
     *
     * @param out the new standard output stream
     *
     * @throws SecurityException
     *        if a security manager exists and its
     *        <code>checkPermission</code> method doesn't allow
     *        reassigning of the standard output stream.
     *
     * @see SecurityManager#checkPermission
     * @see java.lang.RuntimePermission
     *
     * @since   JDK1.1
     */
    public static void setOut(PrintStream out) {
	checkIO();
	setOut0(out);
    }

    /**
     * Reassigns the "standard" error output stream.
     *
     * <p>First, if there is a security manager, its <code>checkPermission</code>
     * method is called with a <code>RuntimePermission("setIO")</code> permission
     *  to see if it's ok to reassign the "standard" error output stream.
     *
     * @param err the new standard error output stream.
     *
     * @throws SecurityException
     *        if a security manager exists and its
     *        <code>checkPermission</code> method doesn't allow
     *        reassigning of the standard error output stream.
     *
     * @see SecurityManager#checkPermission
     * @see java.lang.RuntimePermission
     *
     * @since   JDK1.1
     */
    public static void setErr(PrintStream err) {
	checkIO();
	setErr0(err);
    }

    private static void checkIO() {
        if (security != null)
	    security.checkPermission(new RuntimePermission("setIO"));
    }

    private static native void setIn0(InputStream in);
    private static native void setOut0(PrintStream out);
    private static native void setErr0(PrintStream err);

    /**
     * Sets the System security.
     *
     * <p> If there is a security manager already installed, this method first
     * calls the security manager's <code>checkPermission</code> method
     * with a <code>RuntimePermission("setSecurityManager")</code>
     * permission to ensure it's ok to replace the existing
     * security manager.
     * This may result in throwing a <code>SecurityException</code>.
     *
     * <p> Otherwise, the argument is established as the current
     * security manager. If the argument is <code>null</code> and no
     * security manager has been established, then no action is taken and
     * the method simply returns.
     *
     * @param      s   the security manager.
     * @exception  SecurityException  if the security manager has already
     *             been set and its <code>checkPermission</code> method
     *             doesn't allow it to be replaced.
     * @see #getSecurityManager
     * @see SecurityManager#checkPermission
     * @see java.lang.RuntimePermission
     */
    public static
    void setSecurityManager(final SecurityManager s) {
        try {
            s.checkPackageAccess("java.lang");
        } catch (Exception e) {
            // no-op
        }
        setSecurityManager0(s);
    }

    private static synchronized
    void setSecurityManager0(final SecurityManager s) {
	if (security != null) {
 	    // ask the currently installed security manager if we
 	    // can replace it.
 	    security.checkPermission(new RuntimePermission
				     ("setSecurityManager"));
	}

	if ((s != null) && (s.getClass().getClassLoader() != null)) {
	    // New security manager class is not on bootstrap classpath.
	    // Cause policy to get initialized before we install the new
	    // security manager, in order to prevent infinite loops when
	    // trying to initialize the policy (which usually involves
	    // accessing some security and/or system properties, which in turn
	    // calls the installed security manager's checkPermission method
	    // which will loop infinitely if there is a non-system class
	    // (in this case: the new security manager class) on the stack).
	    AccessController.doPrivileged(new PrivilegedAction() {
		public Object run() {
		    s.getClass().getProtectionDomain().implies
			(SecurityConstants.ALL_PERMISSION);
		    return null;
		}
	    });
	}

	security = s;
	InetAddressCachePolicy.setIfNotSet(InetAddressCachePolicy.FOREVER);
    }

    /**
     * Gets the system security interface.
     *
     * @return  if a security manager has already been established for the
     *          current application, then that security manager is returned;
     *          otherwise, <code>null</code> is returned.
     * @see     #setSecurityManager
     */
    public static SecurityManager getSecurityManager() {
	return security;
    }

    /**
     * Returns the current time in milliseconds.  Note that
     * while the unit of time of the return value is a millisecond,
     * the granularity of the value depends on the underlying
     * operating system and may be larger.  For example, many
     * operating systems measure time in units of tens of
     * milliseconds.
     *
     * <p> See the description of the class <code>Date</code> for
     * a discussion of slight discrepancies that may arise between
     * "computer time" and coordinated universal time (UTC).
     *
     * @return  the difference, measured in milliseconds, between
     *          the current time and midnight, January 1, 1970 UTC.
     * @see     java.util.Date
     */
    public static native long currentTimeMillis();

    /**
     * Copies an array from the specified source array, beginning at the
     * specified position, to the specified position of the destination array.
     * A subsequence of array components are copied from the source
     * array referenced by <code>src</code> to the destination array
     * referenced by <code>dest</code>. The number of components copied is
     * equal to the <code>length</code> argument. The components at
     * positions <code>srcPos</code> through
     * <code>srcPos+length-1</code> in the source array are copied into
     * positions <code>destPos</code> through
     * <code>destPos+length-1</code>, respectively, of the destination
     * array.
     * <p>
     * If the <code>src</code> and <code>dest</code> arguments refer to the
     * same array object, then the copying is performed as if the
     * components at positions <code>srcPos</code> through
     * <code>srcPos+length-1</code> were first copied to a temporary
     * array with <code>length</code> components and then the contents of
     * the temporary array were copied into positions
     * <code>destPos</code> through <code>destPos+length-1</code> of the
     * destination array.
     * <p>
     * If <code>dest</code> is <code>null</code>, then a
     * <code>NullPointerException</code> is thrown.
     * <p>
     * If <code>src</code> is <code>null</code>, then a
     * <code>NullPointerException</code> is thrown and the destination
     * array is not modified.
     * <p>
     * Otherwise, if any of the following is true, an
     * <code>ArrayStoreException</code> is thrown and the destination is
     * not modified:
     * <ul>
     * <li>The <code>src</code> argument refers to an object that is not an
     *     array.
     * <li>The <code>dest</code> argument refers to an object that is not an
     *     array.